This invention pertains to electronic circuits and more particularly to a method and structure for deriving a plurality of signals which are substantially synchronous regardless of where within a large system each signal is derived.
FIG. 1 is a diagram depicting a typical prior art high speed computer system or high frequency measurement system, or the like. In system 100, a signal such as a clock signal is applied to input terminal 99 of driver 101. Driver 101 provides a plurality of signals on leads 104-1 through 104-8, which are typically formed as printed circuit board traces or wiring buses. Naturally, in most systems, the shortest distance between driver 101 and receiver circuits 102-1 through 102-8 which must receive the timing signal have differing propagation delays due to different physical lengths, capacitances, and the like. In the prior art example of FIG. 1, the physical lengths of certain ones of leads 104-1 through 104-8 are adjusted to be longer than the minimum required for electrical connection, in order to insure that all leads 104-1 through 104-8 have substantially equal propagation delays. By providing substantially equal propagation delays, timing edges occur substantially simultaneously at receivers 102-1 through 102-8. In other words, the signal provided by driver 101 arrives at each of receivers 102-1 through 102-8 at the same time such that the arrived signals are substantially synchronous.
Unfortunately, adjusting propagation delays by adjusting the physical lengths of leads 104-1 through 104-8 is expensive, consumes additional space on a printed circuit board, and is somewhat of a hit and miss proposition. Furthermore, the great care and expense required to adjust propagation delays in this manner must be repeated every time the system configuration is changed.
Another prior art technique for attempting to provide a signal having edges occurring substantially simultaneously at a plurality of receiving circuits within a large system is to include propagation delay means other than an additional length of system leads, such as leads 104-1 through 104-8 of the system of FIG. 1. Such propagation delay means are well known in the art and include, for example, the phase lock loop delay means as described in U.S. Pat. No. 4,795,985 on an invention of Gailbreath and assigned to Hewlett Packard Company of Palo Alto, Calif., the assignee of this invention.